In general, a conventional fishing sinker is made of lead material by die casting. Such a fishing sinker can be easily molded to have a variety of shapes in view of the fact that lead is a relatively soft metal and that lead has a great specific gravity. However, lead is a heavy metal hazardous to the human health and can not be easily excreted once it is ingested by the human body. Accidental ingestion of lead into the body of a worker making such a fishing sinker can take place from time to time. In addition, animals, such as birds and fishes, are vulnerable to lead poisoning, which is often fatal. In other words, lead is a potentially dangerous source of environmental pollution, which is getting worse day by day. However, the public is becoming increasingly aware of and concerned about the ecological problems brought about by man-made pollution. In response to such public concern, the applicant of the present invention has successfully developed a fishing sinker made of iron instead of lead, as exemplified in the U.S. patent application Ser. No. 07/946,708 filed by this applicant and later issued as U.S. Pat. No. 5,222,321.
The conventional fishing sinker of lead is generally provided with a through hole large enough to permit a fishing line to pass therethrough. Such a through hole can be made integrally with the lead sinker. However, as far as a fishing sinker of iron is concerned, it is not possible to make economically an iron fishing sinker with an integrally made through hole by punching or forging. The cost of making an iron fishing sinker with a through hole made by drilling can be so high that fishermen are bound to resist using such a sinker. At the present time, a lead fishing sinker with a slender through hole can be made at a low cost only by die casting. In other words, the method of making an iron fishing sinker having a slender through hole at a low cost is not available. In addition, an iron fishing sinker with a slit, in which the fishing line is held, can not be made economically in quantity.